1. Field of the Invention
The present invention generally relates to a magnetic recording/reproducing apparatus and method, and more particularly to a magnetic recording/reproducing apparatus and method having an improved reliability for a reproduced signal by eliminating a deformation in a reproduced signal waveform due to a residual magnetization generated in a magnetic head.
In recent years, since an amount of information processed by a computer system is increased, information recorded by a magnetic disk apparatus is increased. Downsizing and large recording capacity are desired for the magnetic disk apparatus, and thus a magnetic disk apparatus having a high recording density and a high performance are required.
2. Description of the Related Art
FIG. 1 is an illustration of an essential part of a conventional magnetic disk apparatus. In FIG. 1, a magnetic disk 11 comprises a non-magnetic substrate 12, a Cr film 13 formed on the substrate 12 and a magnetic recording film 14 formed on the Cr film 13. The substrate 12 is made of an aluminum plate having a surface processed by means of NiP plating. The magnetic recording film 14 is made of a CoCr film, and has a magnetic anisotropy in a direction longitudinal to a surface of the magnetic disk 11.
A thin-film type magnetic head 21 comprises a non-magnetic substrate 22, a first magnetic pole 23, a coil 25 and a second magnetic pole 26. The non-magnetic substrate 22 comprising Al.sub.2 O.sub.3 acts as a slider. The first magnetic pole 23 comprising a NiFe film is formed on the non-magnetic substrate 22. The second magnetic pole 26 comprising a NiFe film is formed on the first magnetic pole 23 with the coil 25 covered with an insulation film 24 therebetween. A first end of each of the first magnetic pole 23 and the second magnetic pole 26 faces the surface of the magnetic disk 11. The second end of each of the first magnetic pole 23 and the second magnetic pole 26 is connected to each other so that a magnetic flux path is formed. The first magnetic pole 23, the second magnetic pole 26 and the coil 25 are covered with a protective film 27. The magnetic head 21 is so called a ring-magnetic-pole induction type magnetic head.
The first magnetic pole 23 and the second magnetic pole 26 are magnetized by supplying a recording signal current to the coil 25 of the magnetic head 21. A magnetic recording is performed on the magnetic recording film 14 of the magnetic disk 11 by means of a magnetic flux leaking in a gap formed between the first end of each of the first magnetic pole 23 and the second magnetic pole 26.
Additionally, the first magnetic pole 23 and the second magnetic pole 26 are magnetized by a magnetic flux leaking from a magnetized portion of the magnetic recording film 14. Accordingly, reproducing of information can be performed by detecting a voltage signal generated in the coil 25 due to a magnetization of the first magnetic pole 23 and the second magnetic pole 26.
In order to improve a recording/reproducing efficiency of the magnetic head 21, the first magnetic pole 23 and the second magnetic pole 26 are required to have a soft magnetic property.
Additionally, in recent years, a magnetoresistance type thin-film head (MR head) exclusively used as a reproducing head has become of great interest because the MR head can obtain a high reproduction output regardless of a rotation speed of the magnetic disk. A composite thin-film magnetic head is suggested which comprises the ring-magnetic-pole induction type thin-film magnetic head and the MR head integrally formed with each other.
FIG. 2A is an illustration for explaining a conventional composite thin-film magnetic head. FIG. 2B is a partial cross-sectional view of the magnetic head shown in FIG. 2A. FIG. 3 is a bottom view of the magnetic head shown in FIG. 2A.
The composite thin-film magnetic head 30 shown in FIG. 2A comprises an electromagnetic conversion head (recording head) 37 and the MR head 31 (reproducing head). The MR head 31 comprises an MR element 33 formed on a non-magnetic substrate 32, a conductive layer 34 and lower and upper magnetic shielding layers 35a, 35b.
A center portion of the conductive layer 34 is removed in a longitudinal direction, and each end of the conductive layer 34 is connected to the MR element 33. The conductive layer 34 and the MR element 33 are sandwiched between the lower magnetic shielding layer 35a and the upper magnetic shielding layer 35b via non-magnetic insulating layers 36.
The electromagnetic conversion head (inductive head) 37, which performs a recording operation on the magnetic disk 11, comprises the upper magnetic shielding layer 35a as a first magnetic pole, an insulating layer 39, a thin-film coil 40 and an upper magnetic pole 41 as a second magnetic pole. Additionally, the upper magnetic pole 41 is covered with a protective insulating layer 42. A recording gap 38 is formed between an end of the first magnetic pole 35a and an end of the second magnetic pole 41. The recording operation is performed by a magnetic flux formed by the recording gap 38.
FIG. 4 is a cross-sectional view of a conventional MR element and conductive layers. The MR element 33 comprises a soft magnetic layer 33a, a non-magnetic intermediate layer 33b and an MR layer 33c. The soft magnetic layer 33a having a thickness of 300 Angstroms is formed of a soft adjacent layer (SAL) made of NiFeCr. The non-magnetic intermediate layer 33b having a thickness of 100 Angstroms is made of Ta. The MR layer 33c having a thickness of 300 Angstrom is made of NiFe.
A conductive layer 34a is formed on one side of the MR layer 33c, and another conductive layer 34b is formed on the other side of the MR layer 33c. A space of 4 .mu.m is formed as a sensing area between the conductive layers 34a and 34b. The conductive layer 34a comprises an FeMn layer 34a1 formed on the MR layer 33c, a Ta (tantalum) layer 34a2 formed on the FeMn layer 34a1 and a W layer 34a3 formed on the Ta layer 34a2. Similarly to the conductive layer 34a, the conductive layer 34b comprises an FeMn layer 34b1 formed on the MR layer 33c, and a Ta layer 34b2 formed on the FeMn layer 34b1 and a W layer 34b3 formed on the Ta layer 34b2.
The MR head 31 utilizes a resistance of the MR layer 33c which is dependent on a relative angle .THETA. formed between a direction Mn of magnetization according to a magnetic field formed on the magnetic disk 11 and a direction Mi of a sensing current flowing in the MR layer 33c.
That is, a magnetic vector of the MR element 33 is rotated according to the direction of magnetization of the magnetic disk 11, and thereby the resistivity against the sensing current is varied. The resistivity varies in accordance with a square of a cosine of an angle formed between the magnetic vector and a current vector, and thus the resistivity is represented by the following expression. EQU .rho.=.rho.o+.DELTA..rho..sub.max cos.sup.2 .THETA. (1)
where .rho. is resistivity and .DELTA..rho..sub.max is a maximum variation of the resistivity.
According to the above expression, if the directions of magnetization and current are coincident initially, an initial variation of the resistivity due to magnetization of a recording medium is small. Accordingly, the magnetic vector of the MR element is inclined by 45 degrees so that an MR sensor can be used with a high sensitivity and a good linearity.
When the MR sensor passes a magnetized portion of the recording medium, an electric signal is generated according to a sensitivity characteristic of the MR element, and thus a signal recorded on the recording medium can be read.
FIG. 5 is an illustration of an essential part of another conventional magnetic disk apparatus. In FIG. 5, parts that are the same as the parts shown in FIGS. 1 and 2B are given the same reference numerals, and descriptions thereof will be omitted.
A composite thin-film magnetic head 51 shown in FIG. 5 has an additional flux guide 52 positioned between the first magnetic pole 35a and the lower magnetic shielding layer 35b. The flux guide is made of NiFe alloy film. An end of the flux guide 52 faces the magnetic disk 11, and the other end is magnetically connected to the MR element 33.
In the magnetic head 51, a magnetic flux formed on the magnetic disk 11 is supplied to the MR element 33 via the flux guide 52. The provision of the flux guide 52 is to prevent a damage of the MR element 33 or of a surface of the magnetic disk 11 due to a leakage of the sensing current flowing in the MR element when the magnetic head makes a contact with the surface of the magnetic disk 11.
A description will now be given of problems that lie in the conventional magnetic disc apparatus.
In the conventional magnetic disk apparatus having the magnetic head shown in FIG. 1, after a recording operation is performed by supplying electric current to the coil 25, a residual magnetization remains in the first and second magnetic poles 23, 26. Accordingly, when performing a reproducing operation after the recording operation, the reproducing operation is performed in a state where the first and second magnetic poles have the residual magnetization.
In such a case, magnetization of the first and second magnetic poles 23 and 26 according to a magnetic flux generated by a magnetization of the magnetic disk 11 may not be performed smoothly. That is, a reproducing signal waveform obtained by magnetization of the first and second magnetic poles 23 and 26 may have an irregular deformation, and thus an error may be generated in a reproducing signal.
This condition is caused by an irregular and unsmooth movement of a domain wall due to a pinning effect generated by an impurity or a defect and the residual magnetization existing near the end of the magnetic poles. The pinning effect is an irregular movement of the domain wall according to an energy condition due to a blockage of a smooth movement of the domain wall.
This problem happens, in particular, in a combination of a single magnetic-pole type vertical magnetic head and a double-layer construction magnetic disk having a soft magnetic backing layer and a vertical recording layer having a magnetic anisotropy in a vertical direction.
Additionally, there is a problem that a sharp and high level noise, generally called a wiggle noise or a popcorn noise, may be generated due to a movement of the domain wall. This noise is generated when a part of the domain wall suddenly moves from an unstable position to a stable position in a short time after a reproducing operation is started. The wiggle noise is indicated by (a) of a reproducing signal waveform shown in FIG. 6A, and the popcorn noise is indicated by (b) of a reproducing signal waveform shown in FIG. 6B.
In order to eliminate the above-mentioned problems, Japanese Patent Application No. 3-52520 (Japanese Laid-Open Patent Application No. 4-286701) of the present applicant discloses a technique in which a weak current is supplied before starting a reproducing operation so as to move the domain wall from an unstable position to a stable position, and thus preventing generation of the popcorn noise at an initial stage of the reproducing operation.
When the domain wall is pinned by a presence of an impurity or a defect, a current is supplied which is sufficient for generating a magnetic field by which the magnetic poles are magnetically saturated. However, such a current may generate a residual magnetization.
Additionally, since the magnetic field intensity at an end of the magnetic pole is high as the magnetic pole becomes thin toward the end, the generated magnetic field at the end of the magnetic pole may demagnetize a magnetization recorded on the magnetic disk, particularly where a single magnetic pole of a vertical magnetic recording type thin-film vertical magnetic head is used.
Magnetic apparatuses of which magnetic heads are shown in FIG. 2A and FIG. 5 also have the same problems mentioned above. That is, for example, since the flux guide 52 shown in FIG. 5 is adjacent to the first magnetic pole 35a, the residual magnetization is generated due to a magnetic field generated when a recording operation is performed.
FIG.7 is an illustration of an end of the magnetic pole 35a shown in FIG. 5 for explaining the residual magnetization. FIG. 8 is a waveform of a signal output from the MR head 33 shown in FIG. 5.
When the residual magnetization is generated, as shown in FIG. 7, at the end of the magnetic shielding layer 35a (first magnetic pole), and when the residual magnetization is also generated in the flux guide 52, domains in the MR element 31 become irregular and magnetization of the end of the flux guide 52 is not smoothly varied.
In such a condition, a fluctuation is generated in a read waveform of the MR head, and an upper portion and a lower portion of the read waveform become asymmetric. This causes deformation of a reproducing signal Waveform, resulting in an occurrence of an error.
In order to eliminate the above-mentioned problem, the sensing current is adjusted for each MR head provided in a magnetic disk apparatus. However, according to this method, an appropriate current cannot be obtained for each MR head due to tolerance of each MR head, and thus the asymmetry of the read waveform cannot be completely eliminated. Thus, a highly reliable waveform-reproduction system for the MR head cannot be obtained.